diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 311205c8f5ea..46b7f395f1cc 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -1241,18 +1241,36 @@ nsContentUtils::GetParserService()
   return sParserService;
 }
 
+static nsIAtom** sSandboxFlagAttrs[] = {
+  &nsGkAtoms::allowsameorigin,     // SANDBOXED_ORIGIN
+  &nsGkAtoms::allowforms,          // SANDBOXED_FORMS
+  &nsGkAtoms::allowscripts,        // SANDBOXED_SCRIPTS | SANDBOXED_AUTOMATIC_FEATURES
+  &nsGkAtoms::allowtopnavigation,  // SANDBOXED_TOPLEVEL_NAVIGATION
+  &nsGkAtoms::allowpointerlock,    // SANDBOXED_POINTER_LOCK
+  &nsGkAtoms::allowpopups          // SANDBOXED_AUXILIARY_NAVIGATION
+};
+
+static const uint32_t sSandboxFlagValues[] = {
+  SANDBOXED_ORIGIN,                                 // allow-same-origin
+  SANDBOXED_FORMS,                                  // allow-forms
+  SANDBOXED_SCRIPTS | SANDBOXED_AUTOMATIC_FEATURES, // allow-scripts
+  SANDBOXED_TOPLEVEL_NAVIGATION,                    // allow-top-navigation
+  SANDBOXED_POINTER_LOCK,                           // allow-pointer-lock
+  SANDBOXED_AUXILIARY_NAVIGATION                    // allow-popups
+};
+
 /**
  * A helper function that parses a sandbox attribute (of an <iframe> or
  * a CSP directive) and converts it to the set of flags used internally.
  *
- * @param sandboxAttr   the sandbox attribute
- * @return              the set of flags (0 if sandboxAttr is null)
+ * @param aSandboxAttr  the sandbox attribute
+ * @return              the set of flags (SANDBOXED_NONE if aSandboxAttr is null)
  */
 uint32_t
-nsContentUtils::ParseSandboxAttributeToFlags(const nsAttrValue* sandboxAttr)
+nsContentUtils::ParseSandboxAttributeToFlags(const nsAttrValue* aSandboxAttr)
 {
   // No sandbox attribute, no sandbox flags.
-  if (!sandboxAttr) { return 0; }
+  if (!aSandboxAttr) { return SANDBOXED_NONE; }
 
   //  Start off by setting all the restriction flags.
   uint32_t out = SANDBOXED_NAVIGATION
@@ -1266,19 +1284,35 @@ nsContentUtils::ParseSandboxAttributeToFlags(const nsAttrValue* sandboxAttr)
                | SANDBOXED_POINTER_LOCK
                | SANDBOXED_DOMAIN;
 
-// Macro for updating the flag according to the keywords
-#define IF_KEYWORD(atom, flags) \
-  if (sandboxAttr->Contains(nsGkAtoms::atom, eIgnoreCase)) { out &= ~(flags); }
+  MOZ_ASSERT(ArrayLength(sSandboxFlagAttrs) == ArrayLength(sSandboxFlagValues),
+             "Lengths of SandboxFlagAttrs and SandboxFlagvalues do not match");
 
-  IF_KEYWORD(allowsameorigin, SANDBOXED_ORIGIN)
-  IF_KEYWORD(allowforms,  SANDBOXED_FORMS)
-  IF_KEYWORD(allowscripts, SANDBOXED_SCRIPTS | SANDBOXED_AUTOMATIC_FEATURES)
-  IF_KEYWORD(allowtopnavigation, SANDBOXED_TOPLEVEL_NAVIGATION)
-  IF_KEYWORD(allowpointerlock, SANDBOXED_POINTER_LOCK)
-  IF_KEYWORD(allowpopups, SANDBOXED_AUXILIARY_NAVIGATION)
+  // For each flag: if it's in the attribute, update the (out) flag
+  for (uint32_t i = 0; i <  ArrayLength(sSandboxFlagAttrs); i++) {
+    if (aSandboxAttr->Contains(*sSandboxFlagAttrs[i], eIgnoreCase)) {
+        out &= ~(sSandboxFlagValues[i]);
+    }
+  }
 
   return out;
-#undef IF_KEYWORD
+}
+
+/**
+ * A helper function that checks if a string matches (case-insensitive) a valid
+ * sandbox flag.
+ *
+ * @param aFlag  the potential sandbox flag
+ * @return       true if the flag is a sandbox flag
+ */
+bool
+nsContentUtils::IsValidSandboxFlag(const nsAString& aFlag)
+{
+  for (uint32_t i = 0; i < ArrayLength(sSandboxFlagAttrs); i++) {
+    if (EqualsIgnoreASCIICase(nsDependentAtomString(*sSandboxFlagAttrs[i]), aFlag)) {
+      return true;
+    }
+  }
+  return false;
 }
 
 nsIBidiKeyboard*
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index 0bb2f9b4fbe2..587e31112351 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -832,10 +832,19 @@ public:
    * A helper function that parses a sandbox attribute (of an <iframe> or
    * a CSP directive) and converts it to the set of flags used internally.
    *
-   * @param sandboxAttr   the sandbox attribute
-   * @return              the set of flags (0 if sandboxAttr is null)
+   * @param aSandboxAttr  the sandbox attribute
+   * @return              the set of flags (SANDBOXED_NONE if aSandboxAttr is null)
    */
-  static uint32_t ParseSandboxAttributeToFlags(const nsAttrValue* sandboxAttr);
+  static uint32_t ParseSandboxAttributeToFlags(const nsAttrValue* aSandboxAttr);
+
+  /**
+   * A helper function that checks if a string matches a valid sandbox
+   * flag.
+   *
+   * @param aFlag  the potential sandbox flag
+   * @return       true if the flag is a sandbox flag
+   */
+  static bool IsValidSandboxFlag(const nsAString& aFlag);
 
 
   /**
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index b45292183c70..34bcb838be29 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -2864,7 +2864,7 @@ nsDocument::InitCSP(nsIChannel* aChannel)
   NS_ConvertASCIItoUTF16 cspROHeaderValue(tCspROHeaderValue);
 
   // Figure out if we need to apply an app default CSP or a CSP from an app manifest
-  nsIPrincipal* principal = NodePrincipal();
+  nsCOMPtr<nsIPrincipal> principal = NodePrincipal();
 
   uint16_t appStatus = principal->GetAppStatus();
   bool applyAppDefaultCSP = false;
@@ -3036,11 +3036,30 @@ nsDocument::InitCSP(nsIChannel* aChannel)
     // speculative loads.
   }
 
+  // ----- Set sandbox flags according to CSP header
+  // The document may already have some sandbox flags set (e.g., if the
+  // document is an iframe with the sandbox attribute set).  If we have a CSP
+  // sandbox directive, intersect the CSP sandbox flags with the existing
+  // flags.  This corresponds to the _least_ permissive policy.
+  uint32_t cspSandboxFlags = SANDBOXED_NONE;
+  rv = csp->GetCSPSandboxFlags(&cspSandboxFlags);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mSandboxFlags |= cspSandboxFlags;
+
+  if (cspSandboxFlags & SANDBOXED_ORIGIN) {
+    // If the new CSP sandbox flags do not have the allow-same-origin flag
+    // reset the document principal to a null principal
+    principal = do_CreateInstance("@mozilla.org/nullprincipal;1");
+    SetPrincipal(principal);
+  }
+
+
   rv = principal->SetCsp(csp);
   NS_ENSURE_SUCCESS(rv, rv);
 #ifdef PR_LOGGING
   PR_LOG(gCspPRLog, PR_LOG_DEBUG,
-         ("Inserted CSP into principal %p", principal));
+         ("Inserted CSP into principal %p", principal.get()));
 #endif
 
   return NS_OK;
diff --git a/dom/base/nsSandboxFlags.h b/dom/base/nsSandboxFlags.h
index 48cd7306ead9..2026d5cd4d53 100644
--- a/dom/base/nsSandboxFlags.h
+++ b/dom/base/nsSandboxFlags.h
@@ -11,6 +11,11 @@
 #ifndef nsSandboxFlags_h___
 #define nsSandboxFlags_h___
 
+/**
+ * This constant denotes the lack of a sandbox attribute/directive.
+ */
+const unsigned long SANDBOXED_NONE  = 0x0;
+
 /**
  * This flag prevents content from navigating browsing contexts other than
  * itself, browsing contexts nested inside it, the top-level browsing context
diff --git a/dom/interfaces/security/nsIContentSecurityPolicy.idl b/dom/interfaces/security/nsIContentSecurityPolicy.idl
index ab017c86dfbb..703e4237fbfd 100644
--- a/dom/interfaces/security/nsIContentSecurityPolicy.idl
+++ b/dom/interfaces/security/nsIContentSecurityPolicy.idl
@@ -20,7 +20,7 @@ interface nsIURI;
 
 typedef unsigned short CSPDirective;
 
-[scriptable, uuid(68434447-b816-4473-a731-efc4f6d59902)]
+[scriptable, uuid(9454a677-5342-4220-8154-e619410e07e7)]
 interface nsIContentSecurityPolicy : nsISerializable
 {
   /**
@@ -48,6 +48,7 @@ interface nsIContentSecurityPolicy : nsISerializable
   const unsigned short BASE_URI_DIRECTIVE         = 13;
   const unsigned short FORM_ACTION_DIRECTIVE      = 14;
   const unsigned short REFERRER_DIRECTIVE         = 15;
+  const unsigned short SANDBOX_DIRECTIVE          = 16;
 
   /**
    * Accessor method for a read-only string version of the policy at a given
@@ -262,6 +263,17 @@ interface nsIContentSecurityPolicy : nsISerializable
    */
   boolean permits(in nsIURI aURI, in CSPDirective aDir, in boolean aSpecific);
 
+  /**
+   * Delegate method called by the service when the protected document is loaded.
+   * Returns the intersection of all the sandbox flags contained in
+   * CSP policies. This is the most restricting sandbox policy.
+   * See nsSandboxFlags.h for the possible flags.
+   *
+   * @return
+   *    sandbox flags or SANDBOXED_NONE if no sandbox directive exists
+   */
+  uint32_t getCSPSandboxFlags();
+
   /**
    * Delegate method called by the service when sub-elements of the protected
    * document are being loaded.  Given a bit of information about the request,
diff --git a/dom/locales/en-US/chrome/security/csp.properties b/dom/locales/en-US/chrome/security/csp.properties
index 35800705053a..799f6c0c5699 100644
--- a/dom/locales/en-US/chrome/security/csp.properties
+++ b/dom/locales/en-US/chrome/security/csp.properties
@@ -50,6 +50,9 @@ scriptFromStringBlocked = An attempt to call JavaScript from a string (by callin
 # LOCALIZATION NOTE (hostNameMightBeKeyword):
 # %1$S is the hostname in question and %2$S is the keyword
 hostNameMightBeKeyword = Interpreting %1$S as a hostname, not a keyword. If you intended this to be a keyword, use '%2$S' (wrapped in single quotes).
+# LOCALIZATION NOTE (ignoringReportOnlyDirective):
+# %1$S is the directive that is ignore in report-only mode.
+ignoringReportOnlyDirective = Ignoring sandbox directive when delivered in a report-only policy '%1$S'.
 # LOCALIZATION NOTE (notSupportingDirective):
 # directive is not supported (e.g. 'reflected-xss')
 notSupportingDirective = Not supporting directive '%1$S'. Directive and values will be ignored.
@@ -70,3 +73,6 @@ couldntParsePort = Couldn't parse port in %1$S
 # LOCALIZATION NOTE (duplicateDirective):
 # %1$S is the name of the duplicate directive
 duplicateDirective = Duplicate %1$S directives detected.  All but the first instance will be ignored.
+# LOCALIZATION NOTE (couldntParseInvalidSandboxFlag):
+# %1$S is the option that could not be understood
+couldntParseInvalidSandboxFlag = Couldn't parse invalid sandbox flag %1$S
diff --git a/dom/security/nsCSPContext.cpp b/dom/security/nsCSPContext.cpp
index 1fa9aa9653b3..d7a43dcda6a8 100644
--- a/dom/security/nsCSPContext.cpp
+++ b/dom/security/nsCSPContext.cpp
@@ -37,6 +37,7 @@
 #include "prlog.h"
 #include "mozilla/dom/CSPReportBinding.h"
 #include "mozilla/net/ReferrerPolicy.h"
+#include "nsSandboxFlags.h"
 
 using namespace mozilla;
 
@@ -1186,6 +1187,49 @@ nsCSPContext::Permits(nsIURI* aURI,
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsCSPContext::GetCSPSandboxFlags(uint32_t* aOutSandboxFlags)
+{
+  if (aOutSandboxFlags == nullptr) {
+    return NS_ERROR_FAILURE;
+  }
+  *aOutSandboxFlags = SANDBOXED_NONE;
+
+  for (uint32_t i = 0; i < mPolicies.Length(); i++) {
+    uint32_t flags = mPolicies[i]->getSandboxFlags();
+
+    // current policy doesn't have sandbox flag, check next policy
+    if (!flags) {
+      continue;
+    }
+
+    // current policy has sandbox flags, if the policy is in
+    // enforcement-mode (i.e., not report-only) set these flags
+    // and check for policies with more restrictions
+    if (!mPolicies[i]->getReportOnlyFlag()) {
+      *aOutSandboxFlags |= flags;
+    } else {
+      // sandbox directive is ignored in report-only mode, warn about
+      // it and continue the loop checking for an enforcement-mode policy
+      nsAutoString policy;
+      mPolicies[i]->toString(policy);
+
+      CSPCONTEXTLOG(("nsCSPContext::ShouldSandbox, report only policy, ignoring sandbox in: %s",
+                      policy.get()));
+
+      const char16_t* params[] = { policy.get() };
+      CSP_LogLocalizedStr(MOZ_UTF16("ignoringReportOnlyDirective"),
+                          params, ArrayLength(params),
+                          EmptyString(),
+                          EmptyString(),
+                          0, 0,
+                          nsIScriptError::warningFlag,
+                          "CSP", mInnerWindowID);
+    }
+  }
+  return NS_OK;
+}
+
 /* ========== CSPViolationReportListener implementation ========== */
 
 NS_IMPL_ISUPPORTS(CSPViolationReportListener, nsIStreamListener, nsIRequestObserver, nsISupports);
diff --git a/dom/security/nsCSPParser.cpp b/dom/security/nsCSPParser.cpp
index 7bb76d2b6ac7..7cb8c7ceb33d 100644
--- a/dom/security/nsCSPParser.cpp
+++ b/dom/security/nsCSPParser.cpp
@@ -15,6 +15,7 @@
 #include "nsServiceManagerUtils.h"
 #include "nsUnicharUtils.h"
 #include "mozilla/net/ReferrerPolicy.h"
+#include "nsContentUtils.h"
 
 using namespace mozilla;
 
@@ -912,6 +913,39 @@ nsCSPParser::reportURIList(nsTArray<nsCSPBaseSrc*>& outSrcs)
   }
 }
 
+/* Helper function for parsing sandbox flags. This function solely
+ * concatenates all the source list tokens (the sandbox flags) so the
+ * attribute parser (nsContentUtils::ParseSandboxAttributeToFlags) can
+ * use them.
+ */
+void
+nsCSPParser::sandboxFlagList(nsTArray<nsCSPBaseSrc*>& outSrcs)
+{
+  nsAutoString flags;
+
+  // remember, srcs start at index 1
+  for (uint32_t i = 1; i < mCurDir.Length(); i++) {
+    mCurToken = mCurDir[i];
+
+    CSPPARSERLOG(("nsCSPParser::sandboxFlagList, mCurToken: %s, mCurValue: %s",
+                 NS_ConvertUTF16toUTF8(mCurToken).get(),
+                 NS_ConvertUTF16toUTF8(mCurValue).get()));
+
+    if (!nsContentUtils::IsValidSandboxFlag(mCurToken)) {
+      const char16_t* params[] = { mCurToken.get() };
+      logWarningErrorToConsole(nsIScriptError::warningFlag, "couldntParseInvalidSandboxFlag",
+                               params, ArrayLength(params));
+      continue;
+    }
+    flags.Append(mCurToken);
+    if (i != mCurDir.Length() - 1) {
+      flags.AppendASCII(" ");
+    }
+  }
+  nsCSPSandboxFlags* sandboxFlags = new nsCSPSandboxFlags(flags);
+  outSrcs.AppendElement(sandboxFlags);
+}
+
 // directive-value = *( WSP / <VCHAR except ";" and ","> )
 void
 nsCSPParser::directiveValue(nsTArray<nsCSPBaseSrc*>& outSrcs)
@@ -933,6 +967,13 @@ nsCSPParser::directiveValue(nsTArray<nsCSPBaseSrc*>& outSrcs)
     return;
   }
 
+  // For the sandbox flag the source list is a list of flags, so we're
+  // special casing this directive
+  if (CSP_IsDirective(mCurDir[0], nsIContentSecurityPolicy::SANDBOX_DIRECTIVE)) {
+    sandboxFlagList(outSrcs);
+    return;
+  }
+
   // Otherwise just forward to sourceList
   sourceList(outSrcs);
 }
diff --git a/dom/security/nsCSPParser.h b/dom/security/nsCSPParser.h
index ab30ce26c7cc..6d3fffcb9a66 100644
--- a/dom/security/nsCSPParser.h
+++ b/dom/security/nsCSPParser.h
@@ -128,14 +128,15 @@ class nsCSPParser {
     bool            port();
     bool            path(nsCSPHostSrc* aCspHost);
 
-    bool subHost();                                       // helper function to parse subDomains
-    bool atValidUnreservedChar();                         // helper function to parse unreserved
-    bool atValidSubDelimChar();                           // helper function to parse sub-delims
-    bool atValidPctEncodedChar();                         // helper function to parse pct-encoded
-    bool subPath(nsCSPHostSrc* aCspHost);                 // helper function to parse paths
-    void reportURIList(nsTArray<nsCSPBaseSrc*>& outSrcs); // helper function to parse report-uris
-    void percentDecodeStr(const nsAString& aEncStr,       // helper function to percent-decode
+    bool subHost();                                         // helper function to parse subDomains
+    bool atValidUnreservedChar();                           // helper function to parse unreserved
+    bool atValidSubDelimChar();                             // helper function to parse sub-delims
+    bool atValidPctEncodedChar();                           // helper function to parse pct-encoded
+    bool subPath(nsCSPHostSrc* aCspHost);                   // helper function to parse paths
+    void reportURIList(nsTArray<nsCSPBaseSrc*>& outSrcs);   // helper function to parse report-uris
+    void percentDecodeStr(const nsAString& aEncStr,         // helper function to percent-decode
                           nsAString& outDecStr);
+    void sandboxFlagList(nsTArray<nsCSPBaseSrc*>& outSrcs); // helper function to parse sandbox flags
 
     inline bool atEnd()
     {
diff --git a/dom/security/nsCSPUtils.cpp b/dom/security/nsCSPUtils.cpp
index 3727f582b2d7..787ec305fe88 100644
--- a/dom/security/nsCSPUtils.cpp
+++ b/dom/security/nsCSPUtils.cpp
@@ -12,6 +12,9 @@
 #include "nsIStringBundle.h"
 #include "nsNetUtil.h"
 #include "nsReadableUtils.h"
+#include "nsContentUtils.h"
+#include "nsAttrValue.h"
+#include "nsSandboxFlags.h"
 
 #if defined(PR_LOGGING)
 static PRLogModuleInfo*
@@ -672,6 +675,23 @@ nsCSPReportURI::toString(nsAString& outStr) const
   outStr.AppendASCII(spec.get());
 }
 
+/* ===== nsCSPSandboxFlags ===================== */
+
+nsCSPSandboxFlags::nsCSPSandboxFlags(const nsAString& aFlags)
+  : mFlags(aFlags)
+{
+}
+
+nsCSPSandboxFlags::~nsCSPSandboxFlags()
+{
+}
+
+void
+nsCSPSandboxFlags::toString(nsAString& outStr) const
+{
+  outStr.Append(mFlags);
+}
+
 /* ===== nsCSPDirective ====================== */
 
 nsCSPDirective::nsCSPDirective(CSPDirective aDirective)
@@ -974,3 +994,26 @@ nsCSPPolicy::getReportURIs(nsTArray<nsString>& outReportURIs) const
     }
   }
 }
+
+/*
+ * Helper function that returns the underlying bit representation of
+ * sandbox flags. The function returns SANDBOXED_NONE if there is no
+ * sandbox directives.
+ */
+uint32_t
+nsCSPPolicy::getSandboxFlags() const
+{
+  nsAutoString flags;
+  for (uint32_t i = 0; i < mDirectives.Length(); i++) {
+    if (mDirectives[i]->equals(nsIContentSecurityPolicy::SANDBOX_DIRECTIVE)) {
+      flags.Truncate();
+      mDirectives[i]->toString(flags);
+
+      nsAttrValue attr;
+      attr.ParseAtomArray(flags);
+
+      return nsContentUtils::ParseSandboxAttributeToFlags(&attr);
+    }
+  }
+  return SANDBOXED_NONE;
+}
diff --git a/dom/security/nsCSPUtils.h b/dom/security/nsCSPUtils.h
index ed5e90c0fa50..a7c91879113f 100644
--- a/dom/security/nsCSPUtils.h
+++ b/dom/security/nsCSPUtils.h
@@ -74,7 +74,8 @@ static const char* CSPStrDirectives[] = {
   "reflected-xss",   // REFLECTED_XSS_DIRECTIVE
   "base-uri",        // BASE_URI_DIRECTIVE
   "form-action",     // FORM_ACTION_DIRECTIVE
-  "referrer"         // REFERRER_DIRECTIVE
+  "referrer",        // REFERRER_DIRECTIVE
+  "sandbox",         // SANDBOX_DIRECTIVE
 };
 
 inline const char* CSP_CSPDirectiveToString(CSPDirective aDir)
@@ -268,6 +269,19 @@ class nsCSPReportURI : public nsCSPBaseSrc {
     nsCOMPtr<nsIURI> mReportURI;
 };
 
+/* =============== nsCSPSandboxFlag ============ */
+
+class nsCSPSandboxFlags : public nsCSPBaseSrc {
+  public:
+    explicit nsCSPSandboxFlags(const nsAString& aFlags);
+    virtual ~nsCSPSandboxFlags();
+
+    void toString(nsAString& outStr) const;
+
+  private:
+    nsString mFlags;
+};
+
 /* =============== nsCSPDirective ============= */
 
 class nsCSPDirective {
@@ -349,6 +363,8 @@ class nsCSPPolicy {
     inline uint32_t getNumDirectives() const
       { return mDirectives.Length(); }
 
+    uint32_t getSandboxFlags() const;
+
   private:
     nsTArray<nsCSPDirective*> mDirectives;
     bool                      mReportOnly;